Method and Apparatus for Performing Wire Speed Auto-Negotiation

1. An auto negotiation state machine for use by auto negotiation circuitry of a wired Ethernet transceiver that supports communications with an Ethernet link partner at a plurality of rates including a lowest rate and a plurality of higher rates, the state machine comprising: a start state that is entered when reset is asserted, when auto negotiation is disabled, or when auto negotiation is restarted; an idle state that is entered from the start state when reset is deasserted and when auto negotiation is enabled, when in the idle state, the auto negotiation circuitry is operable to: access an abilities register to read the information regarding the plurality of higher rates; write a supported rates variable with the information regarding the plurality of higher rates read from the abilities register; write a qualified supported rates variable with the contents of the supported rates variable; access at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, alter the qualified supported rates variable based upon the downgrade indication variable; perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable; negotiate an agreed link rate with the Ethernet link partner of the lowest rate and the plurality of higher rates; and attempt to establish a link with the Ethernet link partner at the agreed link rate; a link pass state that is entered from the idle state when the attempt to establish the link with the Ethernet link partner is successful; and a link fail state that is entered from the idle state when the attempt to establish the link with the Ethernet link partner is unsuccessful.

2. The auto negotiation state machine of claim 1 , wherein: the agreed link rate is a first link rate that is one of the plurality of higher rates; and in the link fail state, the auto negotiation circuitry is operable to: fail to establish a link with the Ethernet link partner after a predetermined number of link establishment attempts; alter the qualified supported rates variable to exclude the first link rate; negotiate a second link rate with the Ethernet link partner based upon the qualified supported rates variable, wherein the second link rate is less than the first link rate; and attempt to establish a link with the Ethernet link partner at the second link rate.

3. The auto negotiation state machine of claim 1 , wherein: the agreed link rate is a first link rate that is one of the plurality of higher rates; and in the link fail state, the auto negotiation circuitry is operable to: fail to establish a link with the Ethernet link partner after a predetermined number of link establishment attempts; alter the at least one downgrade indication variable to exclude the first link rate; alter the qualified supported rates variable based upon the downgrade indication variable to exclude the first link rate; negotiate a second link rate with the Ethernet link partner based upon the qualified supported rates variable, wherein the second link rate is less than the first link rate; and attempt to establish a link with the Ethernet link partner at the second link rate.

4. The auto negotiation state machine of claim 1 , wherein the link pass state is entered from the link fail state upon establishing a link with the Ethernet link partner.

5. The auto negotiation state machine of claim 1 , wherein: a transition from the link pass state to the idle state occurs when the link with the Ethernet link partner fails; when the idle state is reached from the link pass state upon a failure of the link with the Ethernet link partner, the auto negotiation circuitry is operable to: again write the qualified supported rates variable with the contents of the supported rates variable; again access the at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, again alter the qualified supported rates variable based upon the downgrade indication variable; and again perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable.

6. The auto negotiation state machine of claim 1 , wherein the at least one downgrade information variable comprises: a gigabit mask variable indicating the availability of 1000 BASE-T operations; and a one hundred megabit mask variable indicating the availability of 100 BASE-T operations.

7. The auto negotiation state machine of claim 1 , further comprising a host interface communicatively coupled to the auto negotiation circuitry, wherein: the host interface is operable to receive information from a coupled host; and the auto negotiation circuitry is operable to set the at least one downgrade indication variable based upon the information received via the host interface.

8. The auto negotiation state machine of claim 1 , wherein: a transition from the link pass state to the idle state occurs when the link with the Ethernet link partner fails; when the idle state is reached from the link pass state upon a failure of the link with the Ethernet link partner, the auto negotiation circuitry is operable to: alter the downgrade indication variable based upon a data rate at which the link with the Ethernet link partner failed; again write the qualified supported rates variable with the contents of the supported rates variable; again access the at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, again alter the qualified supported rates variable based upon the downgrade indication variable; and again perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable.

9. The auto negotiation state machine of claim 1 , wherein the abilities register comprises Register 9 as defined in at least the IEEE Std. 802.3, 2000 Edition.

10. The auto negotiation state machine of claim 1 , wherein the start state is also entered when auto negotiation at the plurality of higher rates is precluded.

11. An auto negotiation state machine for use by auto negotiation circuitry of a wired Ethernet transceiver that supports communications with an Ethernet link partner at a plurality of rates including a lowest rate and a plurality of higher rates, the state machine comprising: a start state that is entered when reset is asserted, when auto negotiation is disabled, or when auto negotiation is restarted; an idle state that is entered from the start state when reset is deasserted and when auto negotiation is enabled, when in the idle state, the auto negotiation circuitry is operable to: access an abilities register to read the information regarding the plurality of higher rates; write a supported rates variable with the information regarding the plurality of higher rates read from the abilities register; write a qualified supported rates variable with the contents of the supported rates variable; access at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, alter the qualified supported rates variable based upon the downgrade indication variable; perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable; negotiate an agreed link rate with the Ethernet link partner at a first link rate that is one of the plurality of higher rates; and attempt to establish a link with the Ethernet link partner at the agreed link rate; a link pass state that is entered from the idle state when the attempt to establish the link with the Ethernet link partner is successful; and a link fail state that is entered from the idle state when the attempt to establish the link with the Ethernet link partner is unsuccessful, in the link fail state, the auto negotiation circuitry is further operable to: alter the qualified supported rates variable to exclude the first link rate; negotiate a second link rate with the Ethernet link partner based upon the qualified supported rates variable, wherein the second link rate is less than the first link rate; and attempt to establish a link with the Ethernet link partner at the second link rate.

12. The auto negotiation state machine of claim 11 , wherein in the link fail state, the auto negotiation circuitry is operable to alter the at least one downgrade indication variable to exclude the first link rate.

13. The auto negotiation state machine of claim 11 , wherein the link pass state is entered from the link fail state upon establishing a link with the Ethernet link partner.

14. The auto negotiation state machine of claim 11 , wherein: a transition from the link pass state to the idle state occurs when the link with the Ethernet link partner fails; when the idle state is reached from the link pass state upon a failure of the link with the Ethernet link partner, the auto negotiation circuitry is operable to: again write the qualified supported rates variable with the contents of the supported rates variable; again access the at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, again alter the qualified supported rates variable based upon the downgrade indication variable; and again perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable.

15. The auto negotiation state machine of claim 11 , wherein the at least one downgrade information variable comprises: a gigabit mask variable indicating the availability of 1000 BASE-T operations; and a one hundred megabit mask variable indicating the availability of 100 BASE-T operations.

16. The auto negotiation state machine of claim 11 , further comprising a host interface communicatively coupled to the auto negotiation circuitry, wherein: the host interface is operable to receive information from a coupled host; and the auto negotiation circuitry is operable to set the at least one downgrade indication variable based upon the information received via the host interface.

17. The auto negotiation state machine of claim 11 , wherein: a transition from the link pass state to the idle state occurs when the link with the Ethernet link partner fails; when the idle state is reached from the link pass state upon a failure of the link with the Ethernet link partner, the auto negotiation circuitry is operable to: alter the downgrade indication variable based upon a data rate at which the link with the Ethernet link partner failed; again write the qualified supported rates variable with the contents of the supported rates variable; again access the at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, again alter the qualified supported rates variable based upon the downgrade indication variable; and again perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable.

18. The auto negotiation state machine of claim 11 , wherein the abilities register comprises Register 9 as defined in at least the IEEE Std. 802.3, 2000 Edition.

19. The auto negotiation state machine of claim 11 , wherein the start state is also entered when auto negotiation at the plurality of higher rates is precluded.

20. An auto negotiation state machine for use by auto negotiation circuitry of a wired Ethernet transceiver that supports communications with an Ethernet link partner at a plurality of rates including a lowest rate and a plurality of higher rates, the state machine comprising: a start state that is entered when reset is asserted, when auto negotiation is disabled, or when auto negotiation is restarted; an idle state that is entered from the start state when reset is deasserted and when auto negotiation is enabled, when in the idle state, the auto negotiation circuitry is operable to: access an abilities register to read the information regarding the plurality of higher rates; write a supported rates variable with the information regarding the plurality of higher rates read from the abilities register; write a qualified supported rates variable with the contents of the supported rates variable; access at least one downgrade indication variable; when the at least one downgrade indication variable indicates a higher rates downgrade, alter the qualified supported rates variable based upon the downgrade indication variable; perform auto negotiation with the Ethernet link partner based upon the qualified supported rates variable; negotiate an agreed link rate with the Ethernet link partner of the lowest rate and the plurality of higher rates; and attempt to establish a link with the Ethernet link partner at the agreed link rate; a link pass state that is entered from the idle state when the attempt to establish the link with the Ethernet link partner is successful; and a link fail state that is entered from the idle state when the attempt to establish the link with the Ethernet link partner is unsuccessful, in the link fail state, the auto negotiation circuitry is operable to: fail to establish a link with the Ethernet link partner after a predetermined number of link establishment attempts; alter the at least one downgrade indication variable to exclude the first link rate; alter the qualified supported rates variable based upon the downgrade indication variable to exclude the first link rate; negotiate a second link rate with the Ethernet link partner based upon the qualified supported rates variable, wherein the second link rate is less than the first link rate; and attempt to establish a link with the Ethernet link partner at the second link rate.